This invention relates broadly to position responsive systems and, in particular, position responsive systems of the magnetic type.
Many kinds of position responsive systems are well-known. Typically, these monitor the relative position of a moving object relative to some reference, or control positioning of relatively movable objects by translating motion of the moving object into a feedback signal for closed-loop control of the moving object.
It is also well-known to use magnetic sensing arrangements for such systems. A rather common magnetic sensing arrangement utilizes the principle of the Hall effect. To take advantage of the Hall effect, use is made of a Hall probe or generator, whose output voltage is proportional to the product of the current passing through it and the magnetic field perpendicular to it. Thus, Hall generators have the advantage of providing a voltage output when the transducer is at a standstill. These characteristics facilitate its use in position responsive systems.
In known position controlling systems using Hall probes, the accuracy desired is often difficult to achieve. This is because there are many sources for potential error. One relatively common source is the occurrence of undesired gap variations between the probe and the magnet(s) which field(s) are cut by the former. Such variations can arise from improperly positioning the probe during assembly or, as is more common, shifting of the probe relative to the magnet after use. Another source of error can arise from imperfections in the magnets which affect adversely the reliability of their field strengths.
Efforts have been undertaken to improve accuracy of such position responsive systems. In this regard, reference is made to U.S. Pat. No. 3,329,833, which discloses use of several Hall probes. These are arranged in series with each other and are aligned relative to a sequence of magnetized scale graduations. The Hall probes are regularly spaced from each other by a distance corresponding to one-half period of the magnetized scale indicia to be scanned. The provision of several Hall probes is intended to not only increase total signal voltage, but also permit averaging of the several responses. Averaging, of course, increases accuracy. Such an approach, while minimizing the effect of error, does so at the expense of system simplicity. Moreover, such a system is still subject to errors arising from gap variations between the probes and the magnetic scale.
None of the known position responsive systems of the magnetic type enable precise, real time control or monitoring of the positioning of a pair of relatively movable members despite undesired variations in gap spacings or unreliable field strengths, let alone perform such functions in an economical, efficient and simple manner.